The use of spectrophotometers and spectrofluorimeters to measure the light absorption and emission characteristics of sample materials is well known. Indeed, the basic principles involved are relatively simple. A beam of light, whose characteristics are known, is directed through the sample material and the light that emerges is analyzed to determine which wavelengths of the original beam were absorbed or absorbed and emitted at another wavelength, or otherwise affected, by the sample material. Based on differences between the incident light and the transmitted or emitted light, certain characteristics of the sample material can be determined. The processes of spectrophotometry and spectrofluorimetry, however, while related, proceed from fundamentally different physical principles. Stated simply, spectrophotometry measures the effect the sample material has on the incident beam, whereas spectrofluorimetry measures the effect the incident beam has on the sample material. More particularly, both processes recognize the well-known quantum physics principle that molecules or atoms which are in one quantum energy state may absorb incident photons having particular wavelengths, and thereby be excited into a higher quantum energy state. The now-excited molecule or atom will tend to revert to its ground quantum energy state, either by thermally losing its excitation energy to its surrounding environs or, alternatively, by emitting one or more photons. In the latter case, when emission of the photon is from a singlet quantum state, the process is known as fluorescence. On the other hand, if the photon emission is from a triplet state, the process is known as phosphorescence. Moreover, as is well known, the wavelength of the emitted photon must have a longer wavelength (i.e., less energy) than the incident exciting photon. In its simplest terms, spectrophotometry determines certain sample characteristics by measuring the total amount of incident light which is absorbed, without considering how the absorbing molecules revert back to their ground quantum state. In contrast, spectrofluorimetry determines certain sample characteristics by measuring the fluorescent or phosphorescent properties of a specimen through which light has been directed, to determine certain specimen characteristics. Additionally, the principles underlying spectrofluorimetry may be applied to determine certain characteristics of chemiluminescent and bioluminescent samples. Samples in this genre of material spontaneously emit photons, and hence do not require irradiation with excitation photons in order to induce emission of photons. The principles of sample analysis and evaluation, however, remain unchanged. It will therefore be appreciated that a single spectrofluorimetry device may potentially provide for sample analysis by either exciting sample molecules with external radiation, or by observing the spontaneous photon emission of chemiluminescent or bioluminescent samples.
There is a problem with the above analytic procedures, however, when high solutions of sample material are available in only very small quantities (e.g. 0.5 to 50 micrograms/microliter).
To be effective for spectroscopic measurements, test cuvettes for holding the sample material must be completely filled. This typically requires a substantial amount of sample material or a dilution of the sample material. Consequently, when only a small amount of the sample material is effectively available for testing or if it is desired not to dilute the sample thus ruining it for follow on use, presently available test cuvettes (e.g. 12.5 mm.times.12.5 mm cuvette) are inadequate because of their relatively large size. Merely reducing the size of the cuvette is not the answer. This is so because, with a size reduction of the cuvette, there is also a reduction in the amount of sample material through which light can pass. Consequently, the intensity of the light passing through the sample material is reduced and the sensitivity and accuracy of the measurement is compromised.
The present invention recognizes that it is possible to take spectrofluorescent and spectrophotometric measurements of very small quantities of a sample material, even where there is a relatively high concentration of the material in solution. The present invention recognizes that this can be done by properly focussing collimated light onto the sample material to obtain sufficiently high input light intensities for the desired measurements. Further, the present invention recognizes that this focussing can be accomplished by a device which is engageable, and operatively compatible, with presently available spectrofluorimeters such as the LS-50 Luminescence Spectrometer by Perkin Elmin, or spectrophotometers such as a UVIKON Model 820 spectrophotometer by Kontron.
In light of the above, it is an object of the present invention to provide a micropipette adaptor for spectrographic analysis which allows for spectrofluorescent or spectrophotometric measurements of very small quantities of sample material in solution. Another object of the present invention is to provide a micropipette adaptor for spectrographic analysis which permits recovery of the sample material after spectrographic measurements have been made. Yet another object of the present invention is to provide a micropipette adaptor for spectrographic analysis which allows spectroscopic measurements of samples to be made while the sample is in the process of being transferred in a micropipette. Still another object of the present invention is to provide a micropipette adaptor for spectrographic analysis which provides for a high light collection efficiency to increase the sensitivity of the measurements which are made. Another object of the present invention is to provide a micropipette adaptor for spectrographic analysis which allows a micropipette or other capillary sample holder to be easily installed and removed from the adaptor.